Technical Field
The present invention concerns an apparatus for automatically twisting metal wires, in particular for connecting adjacent, preferably mutually crossing structural elements. The term structural element is used in the context of this invention to denote an elongate body of a round or polygonal, for example quadrangular cross-section. Examples of such structural elements are for example tubes, bars or carriers, as are used in many respects in all fields of industry. Stranded wire bundles, so-called stranded wire cables, or prestressing cables are also viewed as being embraced by the term structural element, being used inter alia for the production of reinforcing cages for prestressed concrete components.
Description of the Related Art
A typical area of use for apparatuses of the kind set forth in the opening part of this specification is the production of such reinforcing cages, for example for prestressed concrete elements. Reinforcing cages have a lattice-like structure comprising (steel) stranded wires. The lattice-like structure is achieved by stranded wires in a first direction and stranded wires in a second direction being arranged in mutually crossing-over relationship. In the region in which they cross each other, the so-called twisting region, the position of the stranded wires relative to each other is fixed by means of a metal wire. The metal wire is laid around the twisting region of the stranded wires, whereby a loop is formed. The two ends of the wire are then twisted relative to each other a plurality of times until the loop of the wire is sufficiently tight to fix the two mutually crossing stranded wires or generally the mutually crossing structural elements relative to each other.
Alternatively to a crossing-over arrangement of a plurality of structural elements, frequently generally adjacent structural elements are fixed by means of twisting wires around the adjacent structural elements. The procedure is implemented with the exception of the differing orientation of the structural elements, substantially as described hereinbefore.
As for example reinforcing cages comprise a large number of stranded wires and accordingly there is also a large number of twisting regions, very many wires have to be twisted for the production of reinforcing cage. Hitherto that has been effected exclusively as a manual operation. As the wires to be used for the twisting operation must also have a certain stability, that activity is exhausting for the persons performing that activity and is also very time-consuming. Because of the manual character of the twisting operation, this also involves irregularly twisted wires. That is admittedly not a serious consideration from the point of view of quality assurance, because of the large number of twistings performed, but a higher degree of reproduction accuracy when twisting wires over adjacent, preferably mutually crossing structural elements, would be desirable.